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In this present work, laser welding experiments were carried out on 1 mm thin Ti6Al4V sheets using a low power Nd-YAG laser machine without using any filler wire and without edge preparation of welding specimens. The influence of different major process control parameters such as welding speed and power on the yield parameters like temperature field, weld bead geometry, microstructure, and mechanical properties are critically investigated. Experimental results are compared in detail with the simulated results obtained using a commercial 3D finite element model. In the simulation model, temperature-dependent thermal and mechanical properties of plates were considered. The temperature readings were recorded with the aid of K type thermocouples. Forced convection has been assumed near weld zone region because of the movement of the shielding gas. Appreciable agreement is found between the experimental and the simulated temperature fields in most of the cases with few exceptions. These deviations on few occasions may be due to the presence of uncertainties inherently present in the experimental domain and uncertainties in the subsequent temperature sensing techniques by the thermocouples. In addition, annealing has been done at 950 °C, 980 °C, and 1010 °C for one selected parameter (192 W, 6 mm/s). The tensile strength of the samples annealed at 980 °C has been found to be 1048 MPa and it is 3% to 4% higher than that of the usual welded samples.

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A three-dimensional elastic-plastic finite element analysis (FEA) is carried out to estimate the rolling contact fatigue (RCF) crack initiation life for varied slip range on the rail arising from operational variations. The wheel load produces Hertzian contact pressure. Variation in engine traction induces slip variations that evolves thermal load in terms of heat flux. The aperiodic rolling of wheel on rail develops non-proportional multiaxial fatigue loading. Present study combines these effects by translating the wheel load on rail for multiple (twelve) pass in presence of thermal load, contact pressure and traction through a proposed simulation. The temperature dependent Chaboche material model with nonlinear kinematic hardening law is implemented to estimate the stresses and plastic strains governing the multiaxial fatigue condition at the interface. The location of maximum von Mises stress, found at a material point on or a layer below the rail-head, contemplates the fatigue crack initiation site. A coded search algorithm helps to identify the critical plane of crack initiation corresponding to the maximum fatigue parameter (FP). In contrast to available predictions of RCF life considering contact pressure and/or traction or frictional heat in isolation, present study combines all these loads together and provides a more realistic result by numerical simulation.

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A finite element-based simulation was carried out to investigate the effects of friction-induced thermal load on rail under varied wheel slip conditions. The surface temperature rise from six different percentage slips (1%, 1.5%, 2%, 5%, 8.5%, and 10%) at the contact interface was examined for eight-wheel pass. The residual stresses and accumulated plastic strains evolved by the effect of localized temperature rise are estimated. Analytical formulation for conduction mode of heat transfer at the contact patch is used to estimate the temperature distribution. The interaction of thermal-elasticplastic field conditions is obtained by a proposed simulation model. This is implemented in commercial finite element software ANSYS 14.0. In order to capture the steep thermal gradient beneath the contact surface, refined mesh is used in the upper layers up to a depth of 2 mm of the simulation domain. For better manifestation of thermally affected material layers, a temperature dependent bilinear-kinematic hardening material condition is applied. Results indicate the maximum temperature rise at about 0.6a from the trailing end in the contact ellipse of semi-major axis a. At higher slippage conditions the initial pearlitic rail steel gets converted to martensite which is often observed on rail surface as white etching layer known to be associated with rolling contact fatigue. The study reveals the mechanisms of thermally induced defects observable on rail surface. The outcomes, in addition, can provide useful information for the development of thermo-mechanically superior rail steels.